Progressive image transmission (PIT) has been widely developed to serve many applications, such as remote image database access, telebrowsing and teleconferencing over relatively low bit-rate channels. In general, transmission of an image file is divided into stages and at the first stage a coarse low resolution image is transmitted as an initial approximation. The resolution of the image is refined by sending more stages. The image is transmitted progressively in order to give a better approximation to the original image.
In the conventional art, many PIT techniques have been proposed and they can be roughly classified into three categories: the pyramidal approach, the transform-based approach and the iterative encoding approach.
In the pyramidal approach, the levels of the pyramid correspond to the successive approximations of the original image. The image can be progressively reconstructed by adding levels of the pyramid to the top level. Reference may be made to: K. H. Tan et al., "Layered image coding using the DCT pyramid", IEEE Trans. Image Process, 4(4), April 1995, pp. 512-516.
In the transform-based approach, the image first undergoes a block transform and the transformed coefficients are transmitted progressively in a certain order, usually from-low-to-high order. In this manner, successive approximation to the original image with progressively high resolution is obtained by inversely transforming the coefficients at each order. Reference may be made to: A. Jain et al., "Scaleable compression for image browsing", IEEE Trans. Consumer Electron, 40(3), August 1994, pp. 394-404.
In the third approach, the residue or difference image of the image file is encoded, either in the spatial domain or in the transform domain. At each stage, an error image or a difference image between the original image and the transmitted image is generated and then encoded at the next stage. Reference may be made to: L. Wang et al., "Lossless progressive image transmission by residual error vector quantization", IEEE Proceedings 135(Pt. F.5), October, 1988, pp. 421-430.
Among the above three approaches, the iterative encoding approach is widely used in the industry due to the fact that the iterative operation can be conducted by a computer at a high speed. The iterative coding approach, however, requires large number of data and thus consumes long operation time.
There is thus a need in the industry to provide a novel iterative coding system for progressive image transmission to enhance the efficiency of processing.
There is also a need to have a simplified iterative coding system for progressive image transmission so that data required in the processing may be reduced.